Ulf Dittmer

Functional Impairment of CD8+ T Cells by Regulatory T Cells during Persistent Retroviral Infection

The establishment of viral persistence generally requires evasion of the host CD8(+) T cell response. Here we describe a form of evasion wherein the CD8(+) T cells are fully capable of recognizing their cognate antigen but their effector functions are suppressed by regulatory T cells. Virus-specific CD8(+) T cells adoptively transferred into mice persistently infected with Friend virus proliferated and appeared activated, but failed to produce IFNgamma or reduce virus loads. Cotransfer experiments revealed that a subpopulation of CD4(+) T cells from persistently infected mice suppressed IFNgamma production by the CD8(+) T cells. Treatment of persistently infected mice with anti-GITR antibody to ameliorate suppression by regulatory T cells significantly improved IFNgamma production by transferred CD8(+) T cells and allowed a significant reduction in viral loads. The results indicate that CD4(+) regulatory T cells contribute to viral persistence and demonstrate an immunotherapy for treating chronic retroviral infections.

Clinical features and virological analysis of a case of Middle East respiratory syndrome coronavirus infection

Summary Background The Middle East respiratory syndrome coronavirus (MERS-CoV) is an emerging virus involved in cases and case clusters of severe acute respiratory infection in the Arabian Peninsula, Tunisia, Morocco, France, Italy, Germany, and the UK. We provide a full description of a fatal case of MERS-CoV infection and associated phylogenetic analyses. Methods We report data for a patient who was admitted to the Klinikum Schwabing (Munich, Germany) for severe acute respiratory infection. We did diagnostic RT-PCR and indirect immunofluorescence. From time of diagnosis, respiratory, faecal, and urine samples were obtained for virus quantification. We constructed a maximum likelihood tree of the five available complete MERS-CoV genomes. Findings A 73-year-old man from Abu Dhabi, United Arab Emirates, was transferred to Klinikum Schwabing on March 19, 2013, on day 11 of illness. He had been diagnosed with multiple myeloma in 2008, and had received several lines of treatment. The patient died on day 18, due to septic shock. MERS-CoV was detected in two samples of bronchoalveolar fluid. Viral loads were highest in samples from the lower respiratory tract (up to 1·2 × 106 copies per mL). Maximum virus concentration in urine samples was 2691 RNA copies per mL on day 13; the virus was not present in the urine after renal failure on day 14. Stool samples obtained on days 12 and 16 contained the virus, with up to 1031 RNA copies per g (close to the lowest detection limit of the assay). One of two oronasal swabs obtained on day 16 were positive, but yielded little viral RNA (5370 copies per mL). No virus was detected in blood. The full virus genome was combined with four other available full genome sequences in a maximum likelihood phylogeny, correlating branch lengths with dates of isolation. The time of the common ancestor was halfway through 2011. Addition of novel genome data from an unlinked case treated 6 months previously in Essen, Germany, showed a clustering of viruses derived from Qatar and the United Arab Emirates. Interpretation We have provided the first complete viral load profile in a case of MERS-CoV infection. MERS-CoV might have shedding patterns that are different from those of severe acute respiratory syndrome and so might need alternative diagnostic approaches. Funding European Union; German Centre for Infection Research; German Research Council; and German Ministry for Education and Research.

Hepatitis B virus suppresses toll-like receptor–mediated innate immune responses in murine parenchymal and nonparenchymal liver cells†

We have previously shown that Toll‐like receptor (TLR)‐activated murine nonparenchymal liver cells [(NPC); Kupffer cells (KC), liver sinusoidal endothelial cells (LSEC)] can suppress hepatitis B virus (HBV) replication. Therefore, the aim of this study was to investigate whether HBV has the ability to counteract the TLR‐mediated control of its replication. Freshly purified murine hepatocytes and NPCs obtained from C57BL6 mice were stimulated by TLR 1‐9 ligands in the presence or absence of hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), HBV virions, or supernatants from HBV‐producing HBV‐Met cells, and HBV replication was suppressed by anti‐ hepatitis B virus X protein (HBx) small interfering RNA (siRNA) in HBV‐Met cells. Supernatants were collected and tested for antiviral cytokines by viral protection assay. HBV gene expression and replication was analyzed by southern blot. RNA and proteins were analyzed by quantitative reverse transcription polymerase chain reaction (RT‐PCR) or western blot and enzyme‐linked immunosorbent assay, respectively. Pretreatment of hepatocytes and NPCs with HBV‐Met cells supernatants, HBsAg, HBeAg, or HBV virions almost completely abrogated TLR‐induced antiviral activity, which correlated with suppression of interferon beta (IFN‐β) production and subsequent interferon‐stimulated gene induction as well as suppressed activation of interferon regulatory factor 3 (IRF‐3), nuclear factor kappa B (NF‐κB), and extracellular signal‐regulated kinase (ERK) 1/2. In HBV‐infected HBV‐Met cells, TLR stimulation did not induce antiviral cytokines in contrast to primary hepatocytes. TLR‐stimulated expression of proinflammatory cytokines [tumor necrosis factor alpha (TNF‐α), interleukin‐6 (IL‐6)], and activation of IRF‐3 was suppressed after up‐regulation of HBV replication in HBV‐Met cells. Accordingly, suppression of HBV replication by siRNA led to activation or expression of proinflammatory transcription factors and cytokines. Conclusion: Our data indicate that HBV can suppress the TLR‐induced antiviral activity of liver cells. This has major implications for the interaction between HBV and the immune system. (HEPATOLOGY 2009.)

Toll‐like receptor‐mediated control of HBV replication by nonparenchymal liver cells in mice

Hepatitis B virus (HBV) infection is one of the most frequent causes of chronic liver disease worldwide. Because recent studies have suggested that Toll‐like receptor (TLR)‐based therapies may be a promising approach in the treatment of HBV infection, we studied the role of the local innate immune system of the liver as a possible mediator of this effect. Murine nonparenchymal cells, including Kupffer cells (KCs) and sinusoidal endothelial cells (LSECs), were isolated from C57/BL6 wild‐type or MyD88−/− mice and stimulated by agonists of TLR1 to TLR9. Supernatants were harvested and assayed for their antiviral activity against HBV in HBV‐Met cells. No direct antiviral effect of TLR agonists could be observed. In controls (myeloid dendritic cells), TLR1, TLR3, TLR4, TLR7, and TLR9 activation lead to production of antiviral cytokines. By contrast, only supernatants from TLR3‐stimulated and TLR4‐stimulated KCs and TLR3‐stimulated LSECs from wild‐type mice were able to potently suppress HBV replication as assessed via Southern blotting. Similar results were found with cells from MyD88−/− mice, indicating that the effect was independent of this signaling pathway. Cellular HBV RNA and hepatitis B surface antigen or hepatitis B e antigen levels in supernatants remained unchanged. Using neutralizing antibodies, we demonstrated that the TLR3‐mediated effect but not the TLR4‐mediated effect is mediated exclusively through interferon‐β. Conclusion: Our data indicate that the innate immune system of the liver can control HBV replication after activation by TLR agonists. This has implications for the development of TLR‐based therapeutic approaches against HBV. (HEPATOLOGY 2007.)

Natural Regulatory T Cells and Persistent Viral Infection

Suppressor T cell is an old term, originally found in the 1970s literature (49, 50), but it was short-lived because advances in molecular biology soon afterward proved that the gene locus, thought to be associated with suppression, was nonexistent. Our recent understanding started with the finding that a small proportion of CD4+ T cells in mice constitutively expressed the high-affinity interleukin-2 (IL-2) receptor α-chain, CD25, and depletion of these cells (now designated natural regulatory T cells [Treg]) caused autoimmune disease and enhanced responses to foreign antigens (112). This study resulted in a rebound of intense interest in suppressor T cells, and similar cells in humans were identified shortly afterward (78, 98; reviewed in reference 9). It is now well established that natural Treg suppress a diverse range of immune responses in a contact-dependent manner in vitro and in vivo, in response to T-cell receptor (TCR)-mediated stimulation (reviewed in references 43 and 136). Human Treg are less well defined than their murine counterparts and less well studied in general, although the two have features in common. Differences between human and murine Treg, which may complicate the interpretation of human data, have been noted. For instance, in naive inbred pathogen-free mice, natural Treg can be reliably isolated based on their CD25 expression; however, this population in adult outbred humans is inevitably a mixture of Treg and recently activated T effector cells, with the latter expected particularly during an ongoing infection. Opinions are divided over whether Treg play a pathogenic role in chronic viral infection in humans, especially in infections for which the development of a vaccine has so far failed, such as in the case of human immunodeficiency virus (HIV) and hepatitis C virus (HCV). This review considers the key findings in Treg biology and discusses the current position for Treg in viral infection, with particular emphasis on the key aspects of persistent viral infections in humans. Other types of suppressor cells, Tr1 and Th3, that suppress via soluble factors independent of cell-to-cell contact have been reviewed recently (106, 107).

The spike-protein of the emerging betacoronavirus EMC uses a novel coronavirus receptor for entry, can be activated by TMPRSS2 and is targeted by neutralizing antibodies

ABSTRACT The novel human coronavirus EMC (hCoV-EMC), which recently emerged in Saudi Arabia, is highly pathogenic and could pose a significant threat to public health. The elucidation of hCoV-EMC interactions with host cells is critical to our understanding of the pathogenesis of this virus and to the identification of targets for antiviral intervention. Here we investigated the viral and cellular determinants governing hCoV-EMC entry into host cells. We found that the spike protein of hCoV-EMC (EMC-S) is incorporated into lentiviral particles and mediates transduction of human cell lines derived from different organs, including the lungs, kidneys, and colon, as well as primary human macrophages. Expression of the known coronavirus receptors ACE2, CD13, and CEACAM1 did not facilitate EMC-S-driven transduction, suggesting that hCoV-EMC uses a novel receptor for entry. Directed protease expression and inhibition analyses revealed that TMPRSS2 and endosomal cathepsins activate EMC-S for virus-cell fusion and constitute potential targets for antiviral intervention. Finally, EMC-S-driven transduction was abrogated by serum from an hCoV-EMC-infected patient, indicating that EMC-S-specific neutralizing antibodies can be generated in patients. Collectively, our results indicate that hCoV-EMC uses a novel receptor for protease-activated entry into human cells and might be capable of extrapulmonary spread. In addition, they define TMPRSS2 and cathepsins B and L as potential targets for intervention and suggest that neutralizing antibodies contribute to the control of hCoV-EMC infection.

The regulatory T-cell response during acute retroviral infection is locally defined and controls the magnitude and duration of the virus-specific cytotoxic T-cell response

Cytotoxic CD8(+) T cells control acute viremia in many viral infections. However, most viruses that establish chronic infections evade destruction by CD8(+) T cells, and regulatory T cells (Treg) are thought to be involved in this immune evasion. We have infected transgenic mice, in which Treg can be selectively depleted, with Friend retrovirus (FV) to investigate the influence of Treg on pathogen-specific CD8(+) T-cell responses in vivo. We observed that Treg expansion during acute infection was locally defined to organs with high viral loads and massive activation of virus-specific effector CD8(+) T cells. Experimental ablation of Treg resulted in a significant increase of peak cytotoxic CD8(+) T-cell responses against FV. In addition, it prevented the development of functional exhaustion of CD8(+) T cells and significantly reduced FV loads in lymphatic organs. Surprisingly, despite the massive virus-specific CD8(+) T-cell response after temporary Treg depletion, no evidence of immunopathology was found. These results demonstrate the important role of Treg in controlling acute retrovirus-specific CD8(+) T-cell responses, and suggest that temporary manipulation of Treg might be a possible therapeutic approach in chronic infectious diseases.

Toll-like receptor-induced innate immune responses in non-parenchymal liver cells are cell type-specific

Little is known of how the Toll‐like receptor (TLR) system can modulate the function of non‐parenchymal liver cells (NPC) as a major component of the innate and adaptive immune system of the liver. To investigate the diversification of TLR signalling pathways in NPC, we isolated Kupffer cells (KC) and liver sinusoidal endothelial cells (LSEC) from wild‐type C57BL/6 mice and examined their responses to TLR1 to TLR9 agonists. The data show that KC respond to all TLR ligands by producing tumour necrosis factor‐α (TNF‐α) or interleukin‐6 (IL‐6), to TLR3 and TLR4 ligands only by producing interferon‐β (IFN‐β), to TLR1 and TLR8 ligands by significantly up‐regulating major histocompatibility complex (MHC) class II and costimulatory molecules, and to TLR1, ‐2, ‐4 and ‐6 ligands by inducing high levels of T‐cell proliferation and IFN‐γ production in the mixed lymphocyte reaction (MLR). Similarly, LSEC respond to TLR1 to ‐4, ‐6, ‐8 and ‐9 ligands by producing TNF‐α, to TLR3 and ‐4 ligands by producing IL‐6, and to TLR3 ligands by producing IFN‐β. Interestingly, despite significant up‐regulation of MHC class II and co‐stimulatory molecules in response to TLR8 ligands, LSEC stimulated by TLR1, ‐2 or ‐6 could stimulate allogeneic T cells as assessed by MLR. By contrast, myeloid dendritic cells, used as positive control for classical antigen‐presenting cells, respond to TLR1, ‐2, ‐4 and ‐9 ligands by both up‐regulation of CD40 and activation of allogeneic T cells. In conclusion, NPC display a restricted TLR‐mediated activation profile when compared with ‘classical’ antigen‐presenting cells which may, at least in part, explain their tolerogenic function in the liver.

Kinetics of CD8+ effector T cell responses and induced CD4+ regulatory T cell responses during Friend retrovirus infection.

Cytolytic CD8+ T cells are critical for the control of acute Friend virus (FV) infection yet they fail to completely eliminate the virus during chronic infection because they are functionally impaired by regulatory T cells (Treg). We performed a kinetic analysis of T cell responses during FV infection to determine when dysfunction of CD8+ T cells and suppressive activity of CD4+ regulatory T cells develops. At 1 week post infection, virus‐specific CD8+ T cells with effector phenotype and cytolytic potential expanded. Peak expansion was found at 12 days post infection, correlating with peak viral loads. After 2 weeks when viral loads dropped, numbers of activated CD8+ T cells started to decline. However, a population of virus‐specific CD8+ T cells with effector phenotype was still detectable subsequently, but these cells had lost their ability to produce granzymes and to degranulate cytotoxic molecules. Contemporaneous with the development of CD8+ T cell dysfunction, different CD4+ T cell populations expressing cell surface markers for Treg and the Treg‐associated transcription factor Foxp3 expanded. Transfer as well as depletion experiments indicated that regulatory CD4+ cells developed during the second week of FV infection and subsequently suppressed CD8+ T cell functions, which was associated with impaired virus clearance.

Rapid development of vaccine protection in macaques by live-attenuated simian immunodeficiency virus.

Convincing data on experimental vaccines against AIDS have been obtained in the simian immunodeficiency virus (SIV) macaque model by preinfection with a virus attenuated by a nef deletion. To investigate the efficacy of a nef deletion mutant of SIVmac32H called pC8 as a live-attenuated vaccine after shorter preinfection periods and to learn more about the nature of the immune protection induced, eight rhesus monkeys were infected intravenously with the pC8 virus. All monkeys became persistently infected, exhibiting low cell-associated viral loads, but strong cellular and, in terms of binding antibodies, strong humoral antiviral responses. Two of eight pC8-infected monkeys developed an immunodeficiency and were not challenged. Sequence analysis of their nef revealed complete replenishment of the deletion. The other six monkeys, two preinfected for 42 weeks and four for 22 weeks, were challenged with pathogenic spleen-derived SIV. Complete protection was achieved in four vaccinees. Virus was consistently detected in two vaccinees from the 22-week-group challenge, however, they remained clinically healthy over a prolonged period. Protection from challenge virus infection or a delayed disease development seemed to be associated with a sustained SIV-specific T helper cell response after challenge. Thus, a sterilizing immunity against superinfection with pathogenic SIV can be induced even after a relatively short waiting period of 22 weeks. Nevertheless, such a vaccine raises severe safety concerns because of its potential to revert to virulence.